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The use of soil sealing indicators in identifying peri urban development
patterns
Georgia Pozoukidou
a*, Myrto Evdou
a, Eldina Valatidou
aa School of Spatial Planning and Development, Aristotle University of Thessaloniki, University Campus, Thessaloniki 54124, Greece
Abstract
EUs 20-20-20 Climate and Energy Strategy recognizes land uses as a critical factor in EU’s emission reduction policies. Therefore, urban areas as a form of intensive land uses, are increasingly considered to have an important role in adaptation and mitigation strategies to reduce greenhouse emissions and limit the negative effects of climate change on the population, economy and environment. Urban development patterns and the associated land uses in terms of their form, function and relation to the natural environment at large spatial scales are in the core of the emission reduction policies. In this context this paper demonstrates how we could utilize soil sealing data provided by the European Environmental Agency in order to compose a land use consumption profile for peri-urban areas that will in turn inform urban development strategies and land use management policies. Based on the use of soil sealing as main input data to identify spatial patterns of urban functions, a set of indices is calculated. The indices are indicative of the variety of land uses allocated in the peri urban areas and efficiency of associated spatial patterns. The study concludes that a set of soil sealing indicators could help us to identify land consumption patterns due to urbanization processes that could in turn inform associated land use and emission reduction policies.
Keywords: land use policies; urban form; soil sealing; spatial patterns
1. Introduction
The EUs 20-20-20 Climate and Energy Strategy is a set of binding legislation to ensure that EU meets the climate and energy strategy for 2020. It sets three key targets which include 20% cut in greenhouse gas emissions (from 1990 levels), 20% of EU energy from renewables and 20% improvement in energy efficiency (EC, 2018a). In addition, under recent EU legislation that was adopted in May 2018, EU Member States have to ensure that greenhouse gas emissions from land use, land use change or forestry are offset by at least an equivalent removal of CO₂ from the atmosphere in the period 2021 to 2030 (EC, 2018b). This legislation derived from the agreement between EU leaders in October 2014 that all sectors should contribute to the EU's 2030 emission reduction target, including the land use sector. Furthermore this commitment is in line with the Paris Agreement and the Kyoto Protocol which point to the critical role of the land use sector in reaching long-term climate mitigation objectives.
It is obvious that land uses have become a critical factor in EU’s emission reduction policies. Therefore, urban areas as a form of intensive land use, are increasingly considered to have an important role in adaptation and mitigation strategies to reduce greenhouse emissions and limit the negative effects of climate change on the population,
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economy and environment (Masson et al., 2014). Hence the land use form or spatial form of urban development and the associated land consumption patterns are within the core of adaptation strategies for resilient cities. Therefore in order to be able to conform to EU Climate and Energy Strategy and create resilient cities we should act proactively by reconsidering urban development patterns and associated land uses in terms of their form, function and relation to the natural environment at large spatial scales. In this context this paper demonstrates how we could utilize soil sealing data provided by the European Environmental Agency (EEA) in order to compose a land use consumption profile for peri-urban areas that will in turn inform urban containment strategies. Based on previous studies on urban sprawl indices (Pozoukidou and Ntriankos, 2017; Jaeger et al., 2010) and the use of soil sealing as
main input data to identify spatial patterns of urban functions, a set of indices is calculated. The indices are indicative of the variety of land uses allocated in the peri urban areas and efficiency of associated spatial patterns.
2. Land uses and resource efficient urban forms
Land uses refer to the allocation of socio-economic activities within the boundaries of a specific location. Main land uses in an urban environment include industry, education, commerce, services, recreation and housing. The interaction of land uses within a spatial entity i.e. a metropolitan area composes the land use system, which can be described by the type, location and spatial features of various land uses (Pozoukidou et al., 2015).
Urban form in turn, is the spatial imprint of a land use system that evolves over time depending on the characteristics and distribution of demand for the socio-economic activities and the differentiation between the demand and supply of land uses (Driessen et al., 1992; Geurs et al., 2004, Pozoukidou et al., 2015). Urban form is not static and rapid urbanization over the last decades brought dramatic changes in cities’ configuration. Dispersed patterns of urbanization became the prevalent spatial development form creating limitless cities. Formal and informal peri urbanization processes are characterized by the displacement of population, industry and main urban services from the city core to the periphery and the creation of new urban cores with their own economic and social dynamics. In Mediterranean cities the peri urban areas consist most of the times of informal non-regularized land use patterns, accompanied by lack of appropriate infrastructure (transportation, sanitation etc.) creating high per capita resource use, land consumption and emissions.
The quest for resource efficient urban forms is not something new. Literature review suggests that there are certain design/planning concepts that are critical to the constitution of sustainable and resource efficient urban forms. These concepts are density, diversity, mixed land use, compactness, transit, and greening (Kenworthy, 2006; Newman and Kenworthy, 2006; Beatley, 2012; Clifton et al., 2008; Jabareen, 2006). Different combinations of these concepts created several well-known urban development strategies such as the compact city, new urbanism, urban containment, transit-oriented development, green urbanism, transit villages, eco city etc., with the underlying common component to reduce land consumption and increase land use efficiency.
3. Measuring land consumption using soil sealing indices
Soil is considered as sealed when the ground is covered by an impermeable material i.e. asphalt, cement etc. Soil sealing is a typical expression of land consumption (Salvati, 2014a) and it determines the loss of soil resources due to urban expansion or occupation of land by urban functions like housing, commerce, roads etc. High percentages of soil sealing are associated to the risks of consumption of fertile agricultural land, flooding, water scarcity and biodiversity endangerment (European Commission, 2012).
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The soil sealing phenomenon is explicitly connected to urban land uses that are expanding at the expense of agricultural land. Given that there will be a rising demand for land resources mainly due to the population growth in urban areas as well as the behavioral preferences associated to westernized living standards makes imperative the mitigation and containment of soil sealing. Recognizing the significance of limiting soil sealing European Commission (EC) adopted in 2007 the Soil Thematic Strategy that presented the soil degradation trends both in Europe and globally, as well as future challenges to ensure soil protection. In an effort to promote good practices for limiting soil sealing, in 2011 EC published a report with an overview of best practices on existing Member State policies and technical measures used to reduce and mitigate soil sealing. In line with this the “Roadmap to a Resource Efficient Europe” (COM(2011) 571) proposes that by 2020, EU policies should take into account their impacts on land use with the aim to achieve no net land take by 2050.
Monitoring the evolution of soil sealing can be a valuable analysis tool for studying land use consumption patterns in urban regions. There have been several indicators developed (Vila 2012; Salvati, 2014b) to study the structure, distribution, fragmentation and variation of soil sealing surfaces with the aim to inform urban containment strategies (Salvati, 2014a) and natural resources protection schemes. To this end European Environment Agency has developed the European soil sealing dataset. The dataset includes a high-resolution map of sealed land covering the whole Europe over time.
Having these data available, the aim of this paper is to demonstrate how to utilize the soil sealing data that is freely available by EEA in order to analyze land consumption patterns and identify peri-urban spatial forms that will in turn be able to inform urban containment strategies and land use management policies.
4. Methodology
4.1 Study area
Located in the eastern part of Thessaloniki’s Urban Agglomeration the study area is composed of three municipalities, the Municipality of Pylaia-Hortiati, the Municipality of Thermi and the Municipality of Thermaikos (fig. 1). The city (urban agglomeration) of Thessaloniki is the second largest city in Greece (after Athens), and one of the largest urban centers in the Balkans. Since the early ‘80s the greater area of Thessaloniki experienced tremendous changes in terms of its morphological and functional organization (Pozoukidou and Ntriankos, 2017). Key development features were the rapid urban expansion and formation of a “new city” that lacked defined boundaries and a center(s). Construction of new high-speed freeways in conjunction with no investments in public transport enhanced the sprawling trend and the location of new shopping centres, research and development (R&D) facilities and companies’ headquarters in the peri-urban area. At the same time, suburban housing became accessible and affordable for middle and low-income families, increasing housing demand and therefore becoming the main form of residential development (Pozoukidou, 2018).
The three municipalities under study absorbed a large part of the recorded urban development in the last 30 years which was either annexed through formal land use plans to existing settlements or was randomly and with no plan located mainly along primary road axis. Therefore, the investigated area is consisted by a complex system of urban land uses and natural areas such as cropland, pastures and woodlands (fig. 2). In addition, the demographic changes in this area are in accordance to the urban developmental trends recorded in the last 30 years where all three municipalities increased their population numbers whereas for the urban center of Thessaloniki a decrease of population was recorded (Pozoukidou and Ntriankos, 2017).
412 Fig. 1. Built and non-built surface map (Urban Atlas, 2012)
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4.2 Soil sealing data and indicators
According to EEA impervious surfaces include impenetrable materials used for construction of roads, parking lots, buildings, rooftops etc. (European Commission, 2012). In 2009 the EEA developed the European soil sealing database, a raster dataset that provides information on the degree of soil sealing ranging from 0% to 100% in a 100x100 meters spatial resolution. In this study the Municipal District (MD) which is the minimum statistical analysis unit for peri-urban areas was used as the spatial analysis unit. Although continuity of space and land use allocation overcomes administrative boundaries the use of MD as spatial analysis unit allowed us to perform comparative analysis of the statistical data and produced soil sealing indicators.
A total of eleven indicators were calculated. These indicators calculated at the MD spatial level from the EEA sealing map. In addition, demographic data was used to relate soil sealing to population numbers within the municipality districts. In specific, for each MD a soil sealing imprint was composed by calculating the amount of land that was occupied by each one of the soil sealing class (SL<10%, 10-30%, 30-50%, 50-80%, >80%). In addition to this five soil sealing classes that were directly provided by the EEA three more indices were calculated in order to better identify the intensity of soil sealing. These were (a) the percentage of land that was occupied by urban functions (industrial, commercial, public, military and private units) which are characterized by 100% soil sealing degree and zero perviousness (UF) (b) the sum of all soil sealing classes (from 1 to >80%) plus the land that was occupied by urban functions (SSLUF) and (c) the percentage of land with 100% perviousness that was composed by uses such as forests, agricultural land, semi-natural areas, green urban areas, wetlands and water (PL).
Furthermore, in an effort to identify the spatial composition of the five soil sealing classes two synthetic indicators were calculated a diversity/entropy index and an evenness index. The diversity index is a quantitative measure that reflects how many different types i.e. soil sealing classes are in a dataset within a spatial unit of analysis i.e. the MD, while it considers how evenly the basic entities (amount of land per soil sealing class in this case) are distributed among those types. The Shannon index is a popular diversity index mainly in the ecological literature, where it is also known as the Shannon Diversity index or the Shannon Entropy index. It is calculated using the following equation:
𝐻
′= − ∑
𝑝
𝑖 𝑅𝑖=1
𝑙𝑛𝑝
𝑖 (1)High values of entropy index indicate high diversity and position variety of soil sealing classes. Furthermore, the Shannon Entropy index can be used to calculate a new index, the evenness index or the Pielou’s index. This index refers to the species evenness i.e. how close in numbers each species in an environment is and is calculated as:
𝐽
′=
𝐻′𝐻′ 𝑚𝑎𝑥(2)Where 𝐻′ is the number derived from the Shannon entropy index and 𝐻′𝑚𝑎𝑥 is the maximum possible value of 𝐻′
(if every species was equally likely), equal to:
𝐻′
𝑚𝑎𝑥= −
∑
1 𝑆 𝑆 𝑖=1𝑙𝑛
1 𝑆(3)
The value of 𝐽′ is constrained between 0 and 1, where less values represent less evenness in the community. Relevant
literature suggests that this index can be used as a measurement of urban primacy (Salvati, Sateriano and Rontos, 2016) with higher values to be associated with more urbanized environments.
Finally, the index of per capita sealed land (PCSL) in square meters was calculated. This index relates the amount of sealed land to the population that resides in the respective area. It has been used in similar studies and values that are greater than 200 m2 are considered as an indicator for low land use efficiency (Salvati, Sateriano and Rontos,
414
5. Results
Land with impervious characteristics (with soil sealing from 1 to 100%, SSLUF index) covers 5.45% of the total study area. Most of this type of land is concentrated in Pylaia (23%) and Mixaniona (21%). This percentage decreases significantly in the MDs of Hortiati (3,5%) and Vasilika (3%) while the values of the rest MDs vary from 5% to 13% (Table1). The percentage of land with 100% perviousness (PL index) presented, as expected, low values in the municipal districts with high impervious surfaces. Calculation of per capita impervious land (PCSL index) which is considered to be a land use efficiency proxy, revealed that Epanomi has the highest value (682 m2) with the rest of
the MDs to be divided into two distinct groups one with low per capita values (Pylaia, Panorama, Hortiatis, Thermaikos) and one with medium values (Mihaniona, Thermi, Mikra, Vasilika). The spatial pattern of PCSL indicates that MDs that are closer to the urban center of Thessaloniki have lower per capita values and therefore present greater land use efficiency.
Table 1. Values of calculated Indicators per Municipal District
Variable Thermaikos Mixaniona Epanomi Thermi Mikra Vasilika Pilea Panorama Hortiatis
<10% 0,00% 0,00% 0,00% 0,00% 0,00% 0,00% 0,00% 0,00% 0,00% 10-30% 0,07% 0,08% 0,04% 0,04% 0,01% 0,02% 0,12% 0,02% 0,08% 30-50% 2,70% 2,89% 1,77% 0,56% 0,33% 0,23% 0,70% 0,39% 0,31% 50-80% 4,02% 7,81% 3,26% 1,44% 2,50% 0,73% 3,15% 2,23% 0,87% >80% 0,15% 0,34% 0,19% 0,23% 0,12% 0,04% 0,90% 0,21% 0,03% UF 5,74% 10,2% 4,08% 10,51% 4,66% 2,26% 18,3% 4,19% 2,10% SSLUF 12,6% 21,3% 9,34% 12,79% 7,62% 3,28% 23,1% 7,04% 3,40% PL 87,21% 78,4% 90,5% 86,5% 92% 96,4% 76,6% 92,8% 95,9% PCSL 160 336 682 225 371 307 100 109 184 DIV 0,80 0,65 0,17 0,71 0,08 0,76 0,96 0,69 0,88 EVAR 0,50 0,41 0,00 0,04 0,05 0,47 0,60 0,43 0,55
The diversity-entropy index (DIV) in combination with Pielou index (EVAR) identifies the MDs with urban functions that are characterized by diversity of impervious surfaces and present features of urban primacy. The spatial distribution of both indices indicate that the most urbanized environments are located close to the prime urban center of Thessaloniki. In specific the MD of Pylaia which is adjacent to Thessaloniki’s Urban Agglomeration is the most urbanized one with DIV 0,96 and EVAR 0,59. The urbanized environment of Pylaia is also confirmed by the high percentage of land with 100% imperviousness (18,32%) which is actually the highest in all 9 MDs under study. The less urbanized MDs that present more rural characteristics are located in the periphery of the study area and present very low values of DIV and EVAR. These are the MDs of Epanomi and Mikra with values of EVAR 0,001 and 0,04
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respectively. Thermi and Mihaniona present less urbanized features than Pylaia with EVAR 0,44 and 0,40 respectively. Their soil sealing profile is composed by relatively high percentages of land dedicated to urban functions (up to 10%) which indicates that these MDs could be playing the role of sub centers in the study area. The rest of MDs, Thermaikos, Vasilika, Panorama and Hortiatis, present the same values of EVAR and DIV as the previous group of MDs but the land dedicated to urban functions is proportionally much less ranging from 4% to 2%. This indicates that they might have urban characteristics but with much less variety of urban functions in their territory.
6. Discussion
The result of the present study suggest that soil sealing indicators calculated using the freely available data provided by EEA, could help us to identify land consumption trends due to urbanization processes. In specific, the procedure followed in this paper concluded to four groups of municipal districts as they emerged by the different index values, which represent the variety of land uses allocated in the peri urban areas as well as the efficiency of associated spatial patterns. The first group includes one MD which presents characteristics of a primary urban center, the second group consists of two MDs presenting strong characteristics of urban sub centers while the third one (4 MDs) present characteristics of emerging urban subcenters. Finally, the fourth group consists of two MDs that present mostly rural characteristics. Last but not least the paper demonstrates that soil sealing data can be used to identify possible transformations in the urban hierarchy and the emergence of important urban centers and sub centers in the peri urban area of large cities. This in turn have several implications in the associated urban containment policies and land use strategies in terms of the proposed land use forms, urban functions and their relation to the natural environment.
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